The proposed research is a systems genetics approach to characterize the complex relationships between genetic variation, epigenetic regulation, gene expression, male reproductive physiology, and environmental exposure. To accomplish this goal, the investigators will leverage the power of diverse inbred mouse strains and the Collaborative Cross, a mouse reference population that has ideal properties for systems genetics. To identify gene-by-environment (GXE) interactions, the investigators will perturb the reproductive system with the powerful estrogen diethylstilbestrol (DES) and phenotype identical exposed and control populations. The investigators will measure DNA methylation, mRNA expression, and reproductive traits with the purpose of modeling genetic effects and GXE across three levels of genome function. This research will produce new biological knowledge of the genetic networks underlying the reproductive system, DES function at the molecular level, and genes underlying DES sensitivity.